Features:

1. Holographic Finish: The tumbler have a holographic finish that creates a shimmering, color-shifting effect reminiscent of underwater mermaid scales.

2. Fish Scale Pattern: The exterior of the tumbler can be adorned with a fish scale pattern, often in shades of blue, green, or other oceanic colors.

3. Large Capacity: With a generous 630ml capacity, this tumbler can hold a substantial amount of your favorite beverage, ensuring you stay hydrated throughout the day.

4. Durability: The tumbler is made from high-quality materials like stainless steel or BPA-free plastic to make it durable and long-lasting.

5. Spill-Proof Lid: A secure, spill-proof lid with a straw opening can make the tumbler convenient for on-the-go use.

6. Easy to Clean: A tumbler with a wide mouth or removable parts is easier to clean, ensuring that it remains hygienic.

7. Non-Slip Base: A non-slip, rubberized base can prevent the tumbler from sliding on surfaces and protect it from accidental drops.

8. Eco-Friendly Materials: If possible, use eco-friendly materials to appeal to environmentally-conscious consumers.

9. Color Options: Offer a range of color choices for the holographic finish, allowing customers to pick their favorite.

10. Easy-Grip Design: An ergonomic shape and textured grip can enhance the tumbler's comfort and ease of use.

11. Unique Design Elements: Consider adding unique mermaid-themed design elements added visual appeal.

12. Box Size: 21x11x11cm